The definition of common or base 10 or Briggsian logarithms is Y = LGT(X) where X = 10^Y. LGT accepts either a COMPLEX or REAL argument and returns a value of the same type.
COMPLEX Arguments
For COMPLEX arguments LGT(Z) is calculated (using complex arithmetic) as
LGT(Z) = LOG(Z)/LOG(10)
The domain of LGT includes all points in the complex plane except the origin. However, intermediate values generated during the calculation of the function can cause overflow or underflow errors for very large or small values of Z.